1. Field of the Invention
The present invention relates to fuel recycling apparatuses and fuel cell systems using the same.
2. Discussion of Related Art
Fuel cells are pollution-free power supply apparatuses, and have therefore been spotlighted as next generation clean energy power generation systems. Power generation systems using fuel cells can be used in self-generators for large buildings, power supplies for electric vehicles, portable power supplies, etc., and can use various fuels, such as natural gas, city gas, naphtha, methanol, waste gas, etc. Fuel cells generally operate on the same basic principle and are classified into molten carbonate fuel cells (MCFCs), solid oxide fuel cells (SOFCs), polymer electrolyte membrane fuel cells (PEMFCs), phosphoric acid fuel cells (PAFCs), alkaline fuel cells (AFCs), etc., according to the electrolyte used.
The polymer electrolyte membrane fuel cells are further classified into polymer electrolyte membrane fuel cell (PEMFCs) or proton exchange membrane fuel cells and direct methanol fuel cells (DMFCs), according to the fuel used.
The polymer electrolyte membrane fuel cell uses a solid polymer as the electrolyte, and therefore, has no risk of corrosion or evaporation due to the electrolyte, and can obtain high current density per unit area. Moreover, since the polymer electrolyte membrane fuel cell has very high output characteristics and low operating temperatures compared to other kinds of fuel cells, it can be used in various applications. For example, the PEMFC has been actively developed as a portable power supply for supplying power to vehicles, etc., a distributed power supply for supplying power to houses or public buildings, etc., and a small power supply for supplying power to electronic equipment, etc.
The direct methanol type fuel cell uses liquid fuel, such as methanol, etc. without a fuel reformer and operates at a temperature less than 100° C. Therefore, the DMFC is suitable for use as a portable power supply or a small power supply.
The polymer electrolyte membrane fuel cell generally includes an anode, an ion selective membrane, and a cathode. The anode and cathode include a catalyst layer, a gas diffusion layer, and a current collection layer. The ion selective membrane permits the transfer of protons, but has high resistivity for electron conduction and anion transfer.
In the polymer electrolyte membrane fuel cell as described above, if fuel, such as pure hydrogen or a methanol aqueous solution, is supplied to the anode, and oxidant, such as air, is supplied, the fuel generates protons and electrons by an oxidation reaction in the catalyst layer of the anode. At that time, the protons move to the cathode through the ion selective membrane, and the electrons move to the cathode through the external circuit. The protons and electrons move to the catalyst of the cathode, where water and heat energy are generated by means of a reduction reaction. Electric energy is then generated by the flow of electrons through the external circuit.
The polymer electrolyte membrane fuel cell as described above uses a solid polymer electrolyte membrane as the ion selective membrane. Therefore, to transfer the protons from the anode to the cathode through the electrolyte membrane, it is the electrolyte membrane must be properly humidified. On the other hand, during operation of the system, the water in the polymer electrolyte membrane fuel cell moves from the anode to the cathode through the membrane, together with the protons. The water is discharged to the outside of the fuel cell by evaporation, condensation, diffusion, etc. Therefore, the polymer electrolyte membrane fuel cell system supplies humidified reactant (fuel and/or oxidant) to the anode and/or cathode to prevent drying out the membrane.
In a general polymer electrolyte membrane fuel cell system, it is very important to manage water. Therefore, the system includes a recycling device, which recycles and reuses the water or the fuel within the fuel cell system, to improve water management and system efficiency within the fuel cell system. However, the recycling device recycles and stores the water and/or the non-reaction fuel and should then supply it to the anode of the fuel cell. Therefore, if the recycling device mounted to the fuel cell system is not able to operate during shaking and rotation, it is difficult to apply it to small or portable fuel cell systems.